crypto: virtio - Remove unused virtcrypto functions

virtcrypto_devmgr_get_first() and virtcrypto_dev_in_use() were added in
2016 by
commit dbaf0624 ("crypto: add virtio-crypto driver")

but have remained unused.

Remove them.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>